What Are Coronal Holes

What are coronal holes?

A) regions in the photosphere where magnetic lines gather, creating cooler areas with much less plasma
B) areas of the corona where magnetic field lines project out into space, allowing charged particles to escape and form the solar wind
C) areas in the corona that allow us to see through to the photosphere
D) tunnels in the outer layers of the Sun that allow photons to escape and form the solar wind
E) all of the above